linux-kernel - Re: [PATCH] ubifs: Fix read out-of-bounds in ubifs_jnl_write

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Message-ID: <135307670.158287.1608717613022.JavaMail.zimbra@nod.at>
Date:   Wed, 23 Dec 2020 11:00:13 +0100 (CET)
From:   Richard Weinberger <richard@....at>
To:     Chengsong Ke <kechengsong@...wei.com>
Cc:     Sascha Hauer <s.hauer@...gutronix.de>,
        linux-mtd <linux-mtd@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        wangfangpeng1@...wei.com, chengzhihao1 <chengzhihao1@...wei.com>
Subject: Re: [PATCH] ubifs: Fix read out-of-bounds in
 ubifs_jnl_write_inode()

Chengsong Ke,

----- Ursprüngliche Mail -----
> The memory area allocated in ubifs_jnl_write_inode() is not aligned with 8
> bytes:
> ino_start = ino = kmalloc(write_len, GFP_NOFS);
> 
> When ino_start passed into write_head -> ubifs_wbuf_write_nolock:
>    n = aligned_len >> c->max_write_shift;
>    if (n) {
>      n <<= c->max_write_shift;
>      err = ubifs_leb_write(c, wbuf->lnum, buf + written, wbuf->offs, n);
>      // Read oob occurs here, read n bytes from buf, and buf is passed from
>      @ino_start which is
>      // not 8 bytes aligned(write_len < n). Program read (n - write_len) more bytes.
>    }
> 
> Reproducer:
> 0. config KASAN && apply print.patch
> 1. mount ubifs on /root/temp
> 2. run test.sh
> 3. cd /root/temp && ls // change atime for link_file
> 4. wait 1~2 minutes
> 
> Cc: <stable@...r.kernel.org>
> Fixes: 1e51764a3c2ac0 ("UBIFS: add new flash file system")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=210865
> 
> Signed-off-by: Chengsong Ke <kechengsong@...wei.com>
> ---
> fs/ubifs/io.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)

Good catch!
Please address the problem in ubifs_jnl_write_inode().
The length there needs to be properly aligned like all other journal
functions do.
I think you managed to trigger the issue because ui->data_len is not aligned.

Thanks,
//richard